Method and device for mapping network headers onto MPLS headers in bearer architectures

ABSTRACT

The invention relates to a method for exchanging information between components in a network by means of terminals which exchange IP information packets over the network, the IP information packets being provided with IP headers having IP addresses. The components include a memory area in which unequivocal terminal identifiers are managed in relation to IP addresses, at least one part of the components in the network being MPLS-enabled and used to route information packets through the network on the basis of MPLS paths and corresponding MPLS headers.

CLAIM FOR PRIORITY

This application claims priority to International Application No.PCT/DE02/03786, which was published in the German language on May 8,2003, which claims the benefit of priority to German Application No. 10152 011.5, which was filed in the German language on Oct. 22, 2001.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a method and device for mapping networkheaders, and in particular, mapping network headers to MPLS headers inbearer architectures.

BACKGROUND OF THE INVENTION

With the introduction of packet-oriented technologies such as UMTS andGPRS, it is to be expected that data transmission will increasingly takeplace wirelessly in future. At the same time the data transmission willnot be restricted to the transmission of voice information, but ratherother services, such as those offered for example on the Internet, willincreasingly be used wirelessly.

At the present time, most mobile radio networks are structured on aconnection-oriented basis. This connection orientation is present atleast between the terminal device and the base station. The backbonenetworks, in contrast, often have a packet-oriented structure. Withvoice and data transmissions in particular, however, the full bandwidthis not needed, since a data transmission takes place only at discreteinstants in time and there is often a long time interval between theindividual, actual information transmissions. Consequently a largeportion of the bandwidth is wasted. Packet-oriented networks have theadvantage that only the required bandwidth is used by packets. In thiscase, the data stream is split up into small packets. A disadvantagewith this approach, however, is that in certain conditions of increaseddemand insufficient bandwidth is available. With voice transmissions inparticular this leads to a considerable loss in quality which manifestsitself in poor sound quality. Quality management is necessary fornetworks of this kind. It is also necessary that the data packets arerouted faster through the network. In order to achieve this, high-speedswitches and routers are required.

In order to cater for the increased data traffic with wirelesssubscribers in the future also, access networks for mobile radionetworks will also be IP-based in future, i.e. there will be an IP-basedtransport network, referred to as the RAN (Radio Access Network),between the base stations and the gateway into the core network.Terminal devices set up a connection via an air interface initially to abase station BS which terminates the air interface. The data of theterminal device MH is then routed by means of an access router AR.Generally the interconnected access routers form the radio accessnetwork. The AR handles the forwarding of the data to the radio accessserver (RAS) or further routers.

Because of the different topologies of the networks a protocol tunnel isoften set up between terminal device MH and access router RAS or betweenAR and RAS as well as between AR and AR. A protocol tunnel is alwayspresent when a first transmission protocol is encapsulated in a secondtransmission protocol. This is referred to as encapsulating the packetsof a first transmission protocol into the packets of the secondtransmission protocol. This is always necessary, for example, if thefirst transmission protocol is not supported on a network segment. Thepacket must then be routed in this network segment with the aid of thesecond transmission protocol. The protocol tunnel provides a number ofadvantages.

For the terminal device, mobility can be supported transparently in thetransport network RAN using any means. This advantage is based on thefact that the packets are not modified and consequently the type andform of the transport can be determined by the topology of the networkwithout any risk of a modification of the user data.

Non IP-based data (e.g. compressed and/or encrypted IP packets, voice)can simply be routed via the transport network RAN to suitableconverters at the edge of the transport network RAN, provided the tunneltechnology used supports the transport of data packets of otherprotocols than IP.

Known methods use tunnels either from the terminal device MH to the RASor from the access router AR to the RAS. Different technologies can beused for this, e.g. PPP, IP-in-IP.

Because of its simple structures and high performance, MultiProtocolLabel Switching (MPLS, IETF Proposed Standard, [RFC3031]) can also beused advantageously as the tunnel technology. In MPLS networks a packettravels from one router to the next. Each router makes an independentdecision with regard to the forwarding of packets. This means that eachrouter analyzes the header of the packet and each router executes aprogram with the router algorithm. Each router selects a new route as afunction of the result of the router algorithm. The selection of thenext route is therefore done in two steps. The first step partitions theentire set of possible packets into a set of forwarding equivalenceclasses (FEC). The second step maps each FEC onto a route. As far as thedecision on the forwarding is concerned, no distinction is made betweenthe packets belonging to the same FEC. Different packets belonging tothe same FEC cannot be differentiated. In this respect the presentinvention is different. In order to be able to use labels as addresses,a unique assignment to an FEC must exist. In other words, an FEC onlyever comprises one label. This label is assigned to one destinationaddress only.

Packets which have a different destination or source address areregarded as different packets. In order to be able to use MPLS for thepresent invention, however, a path and therefore the equivalence classmust be unique. This means that an equivalence class stands for a uniquesource and destination terminal device or entity, and is furtherdescribed below. In an MPLS network the assignment to an FEC is madeonly once, namely at the time the packet enters the network. The FEC towhich a packet is assigned, is coded as a short value which is referredto as a label. When a packet is sent to the next route, the label issent with it. No analysis of the further contents of the packet isperformed at the following routers. Only the label is checked. The labelis used as an index for a table from which the next route and the nextlabel can be retrieved. The old label is replaced by the new label andthe packet is forwarded to the next route. In an MPLS network forwardingis controlled only by means of the labels. This has a number ofadvantages. For example, the routers only need to have limitedcapabilities. They merely need to be able to analyze the label and checkin a table which route is assigned to this label in order to replace theold label by a new label. Furthermore a high throughput can be achievedby these simple tasks. Further advantages can be found in [RFC 3031].

A few principles will be defined in the following. A label is a short,locally significant identifier which has a fixed length and is used toidentify a FEC. The label serves to represent an FEC to which the packetis assigned. In the basic usage of the FEC this is assigned on the basisof the destination addresses of the network layer. In the original usageof the FEC it is not a coding of the network address, however. It is atthis point, as detailed below, that the present invention makes adifference. As a result of the unique assignment of the label to aunique path it is equivalent to the coding of a network address.

In order to ensure that the routers assign the packets to the sameequivalence classes, the routers regularly have to exchange informationfrom which it is clear which packets are assigned to a label. It is alsoimportant that the same labels are not used by different routers,insofar as this makes a unique identification of the preceding routerimpossible. It should further be pointed out that upstreams anddownstreams are handled differently. Thus, for example, these do notnecessarily have the same labels. In the MPLS architecture the decisionto bind a specific label to a specific equivalence class is made by therouter which is located downstream in relation to this binding. Therouter which is downstream then informs the router which is upstreamabout this binding. This information can be transmitted for example aspiggyback information on other packets.

In a further embodiment MPLS supports a hierarchy, whereby theprocessing of the packets provided with labels is totally independent ofthe level of the hierarchy. A packet which has no label can be regardedas a packet whose stack is empty. The use of the stack becomes clearwhen reference is made to the tunneling of packets. Tunneling of thiskind is described in the document [RFC3031]. Packets are always tunneledwhen they are routed through a network path which lies between tworouters, whereby this network path can, in turn, comprise a series ofrouters. If, for example, an explicit path was specified which comprisesthe routers R1 to R4, and if, between the routers R1 and R2, there liesa path which comprises the routers R1.1, R1.2, R1.3, then a furtherlabel is pushed onto the stack by the router R1. The routers R1.1, R1.2,R1.3 now operate on this new second element. As soon as the packetarrives at router R2, the topmost element is popped from the stack. Itbecomes problematical when there is no label on the stack. In the normalMPLS architecture the network address (normally the IP address) isanalyzed in order to determine an equivalence class.

MPLS provides two types of route selection. The first type of routeselection specifies the route already at the starting point. Theindividual routers which have to be passed through are determined. Thisentails a form of explicit routing. With hop-by-hop routing the routersare not specified explicitly, so each router can specify on the basis ofits tables which is to be the next router. The present invention can beoperated with both these methods of route selection.

Existing approaches to using MPLS are based on a use of MPLS in theinterior of the network, for example between access router AR and RAS inthe mobile radio network.

If the terminal device MH switches during ongoing operation from routerARx to router ARy, then it has to re-register with the access router(authentication). With this movement of the terminal device to adifferent base station or another access router, this tunnel is nowswitched to the current anchor point by means of signaling. Toward thatend, however, this must be supported in different variations of theimplementation in the access network IPv6 (IP version 6). As the mappingof such architectures onto existing IP backbones has revealed, a form ofMPLS is mainly supported in this. IP networks are therefore implementedas overlay/VPN (Virtual Private Network) structures and their packetsonly switched quickly, which means less network load and overhead forrouter operation. In a tunneling of the information, however, anoverhead does result in terms of the size of the information packets.IPv6 headers cause more than 40 bytes of header overhead at an averagetransport data size of 60 bytes (IPv6 incl. routing header), the userdata of which in turn comprises only about 20 bytes (VoIP) [RFC 3031,RFC 2460]. Only 4 bytes are induced in each case by means of a shimheader or MPLS header of, for example, MPLS. A shim header, also MPLSheader, comprises further status and administrative information inaddition to the label, which accounts for approx. 20 bits. Basically, aunique identification of the point-to-point link with its attributes,e.g. Quality of Service (QoS), and, of course, the identification of therespective bearer are required.

Known methods for reducing the overhead consist of a compute-intensivecompression technique [RFC2507] (price-rohc-epic-00.txt[www.ietf.org/internet-drafts]) which the individual components orrouters must support. These methods must manage the dynamic statusduring the connection, resulting in the consumption of a lot ofresources (memory, CPU) and therefore imposing limits on the performanceof the components. Where there are a great number of terminal devices(several thousand mobile handsets) which have to be served by acomponent, this can lead to an overloading of the system.

It should however be pointed out that the problems cited are not justrestricted to networks which are operated with mobile terminal devices.Rather, this problem arises whenever different network topologies andarchitectures come into contact with one another and a tunneling ofinformation packets becomes necessary. A limitation of the presentinvention to mobile radio networks is not intended.

SUMMARY OF THE INVENTION

The present invention provides a method which reduces the size of theheaders.

A unique identification of the point-to-point link, in other words theMPLS path, with its attributes (e.g. QoS (Quality of Service)) and, ofcourse, the identification of the respective bearers (connectionservice) are necessary. For this purpose, however, two or more MPLSheaders are to a large extent sufficient, with one of them havingcomponent-related significance. The second can be used dynamicallynetwork-wide, as is usual with MPLS. As a rule this does not result in arestriction only to MPLS (e.g. PPP).

The external MPLS headers are used for identifying the point-to-pointlink and its attributes, as defined in the IPv6 header. These can evenbe modified by the network, if necessary, so long as the link scope isnot destroyed at the end component. The internal headers serve toidentify the bearer, by using parts of a unique terminal deviceidentifier, for example the RNTI [TS 25.331], as used in existingGSM/GPRS/UMTS architectures. This terminal device identifier identifiesthe respective terminal device bearers and is 12 bits, for example, inits short definition (long version 20 bits). Furthermore, several morebits are used in order to allow a flow identification. A shim header orMPLS header provides space for 20 bits per header. A maximum of two shimheaders or MPLS headers are therefore sufficient for one-to-one mappingof the information necessary from IPv6 onto MPLS labels. IPv6-DiffServcan be taken over directly because it is supported in the shim headersor MPLS headers. Compatibility with existing facilities and principlesof operation is maintained since internally the shim headers or MPLSheaders can now once again be uniquely assigned to an IPv6 header or canbe replaced by this, thereby completely preserving the architecturalfeatures and advantages which result from IPv6.

This ensures that a higher efficiency of the network is achieved withthe aid of existing architectural components which preservecompatibility. Usually, for example, the existing RNTI presents itselfas suitable since its 20-bit length enables a direct mapping onto the20-bit label. In the network it is therefore possible to fall back onlabel switching, as a result of which network resources are saved.

Specifically, there is a method for exchanging information betweencomponents in a network which preferably includes a core network and aradio access network.

Components of the network, include, for example, terminal devices whichexchange IP information packets via the network, the packets having IPheaders including IP addresses. The terminal devices are preferablymobile terminal devices, such as mobile phones or PDAs. The terminaldevices have a unique terminal device identifier on the basis of whichthey can be located in the network.

Unique terminal device identifiers in relation to IP addresses areadministered in a memory area. By this means it is possible to map theIP addresses to the terminal device identifiers and vice versa.

The network, for example, has at least a subset of MPLS-capablecomponents which route the information packets through the network onthe basis of MPLS paths and corresponding MPLS headers. In a firstconfiguration step, the components are able to configure themselves suchthat the MPLS paths to the terminal devices are unique, whereby the MPLSpaths are identified at least by means of one mapping as a result of theunique terminal device identifier which is mapped in the MPLS headers.After the components have been configured, the information exchange isperformed in the following steps.

In a second information transmit step the MPLS-capable componentslocated at the start of the path remove the IP headers from the IPinformation packet in order then to provide the thus modified IPinformation packet with MPLS headers. The added MPLS header includes,for example, the terminal device identifier which is administered inrelation to the IP address in order then to transmit the data packetthus modified. In a third information receive step which lies at the endof the path the MPLS-capable components read the MPLS headers of theinformation packets transmitted in the second step in order to determinethe associated IP address on the basis of the terminal deviceidentifier. In this case the IP address is loaded from the abovementioned memory area. This memory area can be a centralized or adecentralized memory area. Thus, for example, it is possible that eachcomponent has its own memory area in which the mapping is stored inreadiness.

After the IP address has been determined, the information packet ismodified such that the original IP header replaces the MPLS header.

Generally the components are known routers which have preferably beenenhanced with suitable hardware components by means of software in orderthereby to implement the above-described functionality.

In an advantageous embodiment, the network is a UMTS or GPRS network ora similar packet-oriented radio network for mobile terminal devices,whereby the terminal device identifiers may include network-specificRAI, RNTI (Radio Network Temporary Identities) or IMSI (furthervendor-specific identifiers are possible). Depending on the chosennetwork, in which these terminal device identifiers are administered ina special register, this is for example an HLR (Home Location Register)or an HSS (Home Subscriber Service). These registers are extended suchthat an IP header and/or an IP address are stored in addition to theterminal device identifier, thereby enabling a unique bijective mapping.

In a further embodiment, the terminal devices themselves are able tohandle the exchange of the headers. In this case, a gateway is used inorder to perform a mapping for the transition into a further externalnetwork which does not support the technology presented. When aninformation packet from the external network arrives the IP header isremoved, and when a packet is transmitted into the external network theIP header is inserted, the communication in the internal network takingplace on the basis of the MPLS headers. The gateway also has access tothe memory area in which the mappings of the IP headers to the deviceidentifiers are stored.

In an alternative embodiment, in addition to the path label the MPLSequivalence classes also include at least one label which codes theterminal device identifier, by means of which it can be establishedwhich path is intended for which terminal device. These equivalenceclasses are preferably the input equivalence classes, i.e. the classeswhich are taken into account when a packet arrives at the component.Through the use of a second label within the MPLS equivalence class itis specified that the terminal device identifier is part of the uniquepath.

In a further embodiment, instead of the entire IP header being removedonly parts of the IP header are removed. This results in less overheadduring the insertion and deletion of the addresses.

In a further advantageous embodiment, a plurality of MPLS labels areused in order to map an IP header onto an MPLS header and vice versa. Acorresponding case has already been described above.

A further component of the invention is a transmitter which implementsthe method described. The transmitter is preferably disposed in anetwork which includes a core network and a radio access network. To theextent that the transmitter is not itself a terminal device, thetransmitter has the switching task of implementing the communication ofterminal devices. The terminal devices exchange IP information packetsvia the network which have IP headers including IP addresses. Thetransmitter comprises a device which permit access to a memory area inwhich unique terminal device identifiers are administered in relation toIP addresses. The device preferably comprise a network interface, to theextent that the memory area is administered by a central server. If, onthe other hand, the device comprises a decentralized memory area whichis administered by the transmitter itself, then the device is usuallymemories, controllers and microprocessors or a special chipset which isoptimized for memory access.

The transmitter further comprises a device which route the informationpackets through the network on the basis of MPLS paths and correspondingMPLS headers. The device is preferably known switching fabrics such asthose belonging to the prior art.

In still another embodiment, there is a processing unit which ispreferably embodied as a processor or as a switching fabric removes IPheaders from the IP information packet in order to provide the thusmodified IP information packet with MPLS headers, whereby the MPLSheader includes the terminal device identifier which is administered inrelation to the IP address. The data packets modified in this way arethen transmitted via the corresponding MPLS path to the terminal device.

In certain circumstances it may be necessary for the device accessingthe memory to load the corresponding address or the header from thememory area.

In order to configure the unique paths to the terminal device in advanceor to set up the equivalence class, a device is provided whichconfigures the transmitter in such a way that the MPLS paths to theterminal devices are unique, whereby the MPLS paths are identified bythe unique terminal device identifier which is mapped in the MPLSheaders. The device preferably comprises a network interface and acorresponding processing unit which is either a microprocessor or theswitching fabric. Typically, known modules are enhanced by suitablesoftware in such a way that the required functionality can beimplemented.

In a preferred embodiment in which the memory area is administerednon-centrally at the transmitter, the terminal device identifiers areassigned to the corresponding MPLS equivalence classes, the terminaldevice identifiers already being coded as MPLS labels or MPLS headers.

In addition to the transmitter, a receiver is a further component andembodiment of the present invention. The receiver is a suitablecounterpart to the transmitter. It is therefore disposed in the samenetwork. It should be pointed out that the receiver and the transmitterare typically routers which represent the input and the output of anMPLS path. The components which are located within the path do not needthe extended functionality. The receiver likewise has a device whichpermits access to a memory area in which unique terminal deviceidentifiers are administered in relation to IP addresses.

The device can comprise elements which enable centralized as well asdecentralized or local access to the memory area. Usually these are thesame device as those used for the transmitter.

The receiver further comprises a device which receives the informationpackets from the network on the basis of MPLS paths and correspondingMPLS headers. Typically, they comprise a network interface having asuitable driver, the packets received in this way being forwarded to theprocessing unit.

The processing unit analyzes the information packets in order todetermine whether the IP header has been removed. If this were to be thecase, in the positive case the associated IP address is determined onthe basis of the terminal device identifier by a memory access in orderthat the information packet can then be modified such that the originalIP header replaces the MPLS header.

This processing unit too is preferably a known switching fabric and/or amicroprocessor which have been enhanced with the necessary functionalitywith the aid of a suitable software solution.

Further components of the receiver include a device which configures thereceiver in such a way that the MPLS paths to the terminal devices areunique, the MPLS paths being identified by the unique terminal deviceidentifier which is mapped in the MPLS headers. This is a similar deviceas in the case of the transmitter, whereby, however, the equivalenceclasses are determined which are to be taken into account when theinformation packets arrive.

In a decentralized solution the terminal device identifiers are coded asMPLS labels and assigned to a specific equivalence class whichdetermines the unique path to the terminal device.

Typically, routers or gateways have the features of both a transmitterand a receiver. In a further embodiment, in which the MPLS paths extendas far as immediately up to the terminal device, the terminal device hasthe described features of the transmitter and the receiver. In anoptimized version the conversion of the IP addresses is then no longernecessary provided the communication takes place in a homogeneousnetwork. A conversion or mapping is necessary only if the network isleft by a gateway.

BRIEF DESCRIPTION OF THE DRAWINGS

The process is represented schematically below with reference tofigures, in which:

FIG. 1 shows a network including a core network and a radio accessnetwork having a transmitter.

FIG. 2 shows information packets during the different transmissionstates, whereby the optimized transmission takes place after anacknowledgement by an Acknowledge packet.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a basic structure of a network in the radio area. In thiscase a network architecture 10 includes a radio access network 16 and acore network 15. The core network 15 can set up the connection to theInternet via a gateway/router 19. Both networks includes a number ofcomponents 19, 13, 12, 14.

A User Plane Server (UPS) 14 administers the radio protocol 20 in orderto transport information packets to the terminal device 11 via radiointerfaces. A Radio Control Server (RCS) 16 administers the frequencyband and permits the allocation or denies the allocation of frequenciesif a bottleneck should arise. These two components, which also haverouter functionalities, form the radio access network 16 together withthe corresponding cable connections 21.

The core network in turn comprises routers 19 which are connected to theUPS. An HLR (Home Location Register) 13 administers the uniqueidentifier of the terminal device and its current position. The HLR 13further comprises the mapping of the IP address to the MPLS headers orlabels. In the present example this mapping is stored at a decentralizedlocation. The transmitter 27 and the receiver 28 have access to thisregister.

As a rule, however, this position is merely a region indication. TheHLR/HSS further administers the call numbers and the current IP address.

The components of the core network and the radio access network areconnected to one another via fiber optic or copper cable 21. It ishowever possible that these components are in contact with one anotherby a radio relay link.

A transmitter 27 receives an information packet 22 which has an IPheader 25. The IP address is used to determine the device identifier,which in the present case is coded in two MPLS headers 24. These MPLSheaders reside in the stack in the information packet 22, whichexclusively comprises MPLS headers.

The transmitter 27 removes the IP header 25 and adds further informationwith the result that the data area 29 is made bigger. The thus modifiedpacket 26 is forwarded to the receiver 28 via a further router whichmodifies the first MPLS header in accordance with the standard. Thereceiver 28 then removes the MPLS header 24 and replaces it with an IPheader. The receiver establishes the correct IP header on the basis ofthe information which is stored in the register 13. In an alternativeembodiment, this information can also be stored locally at the receiver.

The methods for exchanging the mapping have already been describedabove. Because of the varying data area 29 it can happen that a numberof packets are combined or split apart. A suitable numbering of thesepackets is part of the prior art.

FIG. 2 shows a transmission method in which four states are described.These four states mirror the communication in the network. In the firststate the transmission takes place in the form of tunneled IP packets.During the second state a further label is inserted which is intended toreplace the IP address in future. This label can code the RNTI. Otherunique identifiers are also possible. An end-to-end transmission takesplace in the fourth state, after the distant station, in other words thereceiver, has sent an acknowledgement 30 in which it confirms that themapping has been learned.

1. A method for exchanging information between components in a networkwhich includes a core network and a radio access network, havingterminal devices which exchange, via the network, IP information packetswhich have IP headers including IP addresses, having a memory area inwhich unique terminal device identifiers are administered in relation toIP addresses, comprising: routing, via at least one subset ofMPLS-capable components in the network, the information packets throughthe network based on MPLS paths and corresponding MPLS headers;configuring the components such that the MPLS paths to the terminaldevices are unique, the MPLS paths being identified by the uniqueterminal device identifier which is mapped in the MPLS headers;removing, via the MPLS capable components, at least part of the IPheaders from the IP information packet to provide modified IPinformation packet with MPLS headers, the MPLS header including theterminal device identifier which is administered in relation to the IPaddress to send the modified data packet; and reading, via theMPLS-capable components, the MPLS headers of the information packetssent to determine an associated IP address based on the terminal deviceidentifier to modify the information packet such that the original IPheader replaces the MPLS header.
 2. The method according to claim 1wherein the components function as a router.
 3. The method according toclaim 1, wherein the network is a UMTS or GPRS or a similarpacket-oriented radio network for mobile terminal devices, wherein theterminal device identifiers include network-specific RAI, RNTI or IMSIand further identifications.
 4. The method according to claim 1, whereinthe memory area in which the terminal device identifier is stored is anHLR or HSS.
 5. The method according to claim 1, wherein the terminaldevice identifiers are stored in the memory area in relation to the IPheaders and/or IP addresses.
 6. The method according to claim 1, furthercomprising removing the IP header, via a gateway to an external network,when an information packet arrives from the external network, andinserting the IP header when a packet is transmitted into the externalnetwork, the communication in the internal network taking place based onthe MPLS headers.
 7. The method according to claim 1, wherein the MPLSequivalence classes include at least one label which codes the terminaldevice identifier, by which it can be determined which path is intendedfor which terminal device.
 8. The method according to claim 1, wherein aportion of the IP header is removed.